In a conventional mobile communication system, in an uplink from a mobile station UE to a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel, in consideration of radio resources of the radio base station Node B, an interference volume in an uplink, transmission power of the mobile station UE, transmission processing performance of the mobile station UE, a transmission rate required for an upper application, and the like, and to notify the determined transmission rate of the dedicated channel by a message in a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 11, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of channel (for example, per approximately 1 through 100 ms), due to processing load, processing delay, or the like.
In addition, in the conventional mobile communication system, there has also been a problem that costs for implementing an apparatus and for operating a network are substantially increased even ff the fast control for changing of the transmission rate of the channel can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the channel is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 12(a), the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 12(b), or, as shown in FIG. 12(c), by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIG. 12.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
As disclosed in the non-patent document 1, in a conventional mobile communication system using the “enhanced uplink,” the mobile station UE is configured to decrease the current transmission rate of uplink user data when the mobile station UE receives a relative transmission rate control channel (a relative grant channel: RGCH) instructing to decrease the transmission rate of uplink user data (that is, including a “Down” command) from the radio base station Node B.
Moreover, as disclosed in the non-patent document 1, an HARQ protocol is applied to the conventional mobile communication system using the “enhanced uplink.” Accordingly, the radio base station Node B is configured to transmit a positive transmission acknowledgement signal (Ack) to the mobile station every time a reception/decoding processing on each of the transmission data blocks included in the uplink user data has been successful. In contrast, the radio base station Node B is configured to transmit a negative transmission acknowledgement signal (Nack) to the mobile station when the reception/decoding processing has not been successful.
The mobile station UE is configured to continue retransmission of the same transmission data block until a positive transmission acknowledgment signal (Ack) is received at the mobile station UE, or until the number of retransmissions reaches the maximum retransmission number predetermined by the radio network controller RNC.
Here, when the mobile station UE has received a “Down” command via the RGCH, the mobile station UE is configured to decrease the transmission rate of the uplink user data regardless of “Ack/Nack/DTX” on an HICH.
Meanwhile, the radio base station Node B is configured to determine an increase or decrease of the transmission rate of the uplink user data, regardless of the result of a reception/decoding processing of the transmission data block, and to notify the determined result (an “Up” command or a “Down” command) to the mobile station UE via the RGCH.
In the conventional mobile communication system using the “enhanced uplink”, when the radio base station Node B transmits the negative transmission acknowledgment signal (Nack) due to a reception error at the radio base station Node B, the mobile station UE continues retransmission unless a reception error of “Ack/Nack” on the HICH occurs. Hence, the transmission rate of the uplink user data remains unchanged.
However, there has been a problem that, if the mobile station UE assumes a “DTX” included in the RGCH as the “Down” command, the mobile station UE decreases the transmission rate of the uplink user data, thereby a decrease unintended by the radio base station Node B in the transmission rate occurs.
Non-patent Document 1: 3GPP TSG-RAN TS25.309 V6.2.0